This invention relates generally to a multi-winding electric power supply and, it relates more particularly to a system, method, and computer software code for controlling multiple alternators.
Propulsion systems for traction vehicles, such as but not limited to locomotives and off-highway vehicles, commonly use a diesel engine prime mover to drive an electric generating system for supplying energy to a plurality of pairs of direct current (DC) traction motors. The generating system typically includes a 3-phase traction alternator whose alternating voltage output is rectified and applied to relatively positive and negative DC buses between which the respective pairs of motors are connected in parallel. The output power of the alternator is regulated, or varied, by suitably controlling the strength of its field excitation and the rotational speed of the engine. For maximum efficiency, the controls of the propulsion system are suitably designed to work the engine on its full horsepower curve throughout a wide speed range of the vehicle.
FIG. 1 discloses a prior art circuit illustrating a cranking scheme and traction alternator regulation for a powered system, such as but not limited to a locomotive. This cranking scheme is generally used with DC locomotives. Two groups of power electronics and corresponding control micro-electronics are disclosed. The two groups have identical power electronics sections and similar micro-electronics sections. The power electronics section of each group may be a rectifier bridge 12, 14 or other rectifier-type device, formed of a plurality of silicon- or semiconductor-controlled rectifiers (SCR) or other power components. A first bridge 12 is a 3-phase full wave rectifier bridge (3 pairs of SCRs—6 SCRs in total—3 legs). A second bridge 14 is a 3rd harmonic commutation inverter, comprised of a similar 3-phase full wave rectifier bridge. The second bridge 14 and an additional auxiliary commutation leg (4th leg) 20 (with a similar pair of SCRs), form a converter (4 pairs of SCRs—8 SCRs in total—4 legs). The first bridge 12, or first group of SCRs, or first group of power electronics, is connected to an auxiliary alternator or other generator 16 (occasionally referred to herein as the second generator). A traction alternator controller (TAC) central processor unit (CPU) card 18 (referred to as the “TAC Control CPU Card” in FIG. 1) is used to control the operation of the first bridge 12. The second bridge 14 is connected to a main traction alternator or other rotatable synchronous generator 22 (occasionally referred to herein as the first generator). A cranker controller CPU card 24 (referred to as the “Cranker Control CPU Card” in FIG. 1) is used to control the second bridge 14. The two controllers 18, 24 operate alternatively, where only one controller operates at any given time. More specifically, the cranker controller 24 is generally used when starting an engine and the traction alternator controller 18 is generally used while the engine is operating to provide power to auxiliary subsystems on the locomotive.
The cranker controller 24 typically provides control firing pulses for a current-fed, third harmonic commutation SCR inverter (e.g., the second bridge 14), thus supplying variable frequency alternating current to the 3-phase stator windings of the first generator 22 and DC current for the machine field, which is used to start or “crank” the engine. Specifically, the first generator 22 is operated as a motor and the rotor of the generator is coupled to the crankshaft of the engine to rotate the crankshaft for starting. Initially the output torque of the rotor (and hence the magnitude of current in the stator windings) needs to be relatively high in order to start turning the crankshaft. As the rotor accelerates from rest, less torque (and current) will be required, while the fundamental frequency of load current increases with speed (revolutions per minute). In its cranking mode of operation, the cranker controller 24 is responsible for varying the firing commands for the second bridge 14, thus supplying current of properly varying magnitude and frequency until the engine crankshaft is rotating at a rate that equals or exceeds the minimum speed at which normal running conditions of the engine can be sustained.
The first bridge 12 and second bridge 14 may be a third harmonic auxiliary impulse commutated converter having six main unidirectional conduction controllable electric valves, such as thyristors, that are interconnected in pairs of series aiding alternately conducting valves to form a conventional 3-phase, double-way, 6-pulse bridge between a pair of DC terminals, and a set of three AC terminals. During cranking the DC terminals of each bridge 12, 14 are adapted to be connected to an on-board locomotive battery 27. The AC terminals of the aforesaid bridges 12, 14 are respectively connected to the different phases of a 3-phase electric load circuit, which typically comprises the star-connected 3-phase stator windings of each respective generator 16, 22.
As illustrated, gates 25, or switches, are provided to connect/disconnected the battery 27. As further illustrated, the battery 27 is connected to inductors 29 and resistors 31. The inductors 29 are power storage devices and the resistors 31 regulate current. Those skilled in the art will readily recognize that the illustrated configuration of the inductors 29 and resistors 31 is not limiting. Other configurations may be utilized to regulate current and store power, and other components, such as but not limited to a variable diode, may also be utilized. Further, the number of inductors 29 and resistors 31 may vary as well.
With respect to both the main traction alternator 22, or first generator, and the auxiliary alternator 16, or second generator, when supplying the load circuit with 3-phase alternating current, the six main valves of each respective bridge 12, 14 are cyclically turned on (i.e., rendered conductive) in a predetermined sequence in response to a family of “firing” signals (e.g., gate pulses) that are periodically generated in a prescribed pattern and at desired moments of time by associated controllers, specifically a traction alternator controller 18 with respect to the first bridge 12 and the cranker controller 24 with respect to the second bridge 14. With respect to the main traction alternator 22, or first generator, to periodically turn off the main valves by forced commutation, the cranker controller 24 with the second bridge 14 are further provided with an auxiliary commutation leg 20, or the 4th pair of SCRs, that includes a pre-charged commutation capacitor 26 and at least seventh and eighth alternately conducting unidirectional controllable electric valves that are arranged to connect the capacitor 26 between the neutral or common point of the 3-phase AC load circuit and either one of the DC terminals of the bridge.
When systems are composed of multiple elements, a preference is to reduce a number of elements that are part of any given system. This desire is further preferred when redundant elements are provided to perform similar functions. Towards this end, locomotive operators and owners would benefit from having a minimum number of parts for use with both the power electronics used with the locomotive's auxiliary alternator and the main traction alternator. Likewise, operators and owners of other powered systems that utilize multiple power generators having duplicate parts would realize a financial benefit from having a minimum number of parts for the power electronics used for both an auxiliary alternator and a main alternator.